1. Field of the Invention
The present invention relates to a procedure for fully automatic cylinder cleaning in printing machines with a central control system.
2. Background of the Related Art
Printing machines are taken to be newspaper rotary presses, jobbing rotary presses and sheet-fed printing presses, for all printing processes, such as offset printing, Anilox offset, intaglio printing, flexographic printing, Anilox-flexographic printing, relief printing, and photogravure printing. The cylinders to be cleaned are understood to be all of the rollers, rolls, and cylinders, in particular rubber-blanket [offset] cylinders, inking cylinders, plate cylinders, cooling rollers, guide rollers, ink rollers, and damping rollers.
Common to all of these presses is the fact that intensive contact is required between the material to be imprinted and the cylinders in order to guide, process, and drive sheets or webs that are to be imprinted. Because of this, deposits of paper dust, printing ink, and sometimes powder dust build up on the cylinders. These deposits prevent the cylinders from functioning correctly; for example, deposits on rubber-blanket cylinders have a deleterious effect during offset printing: the sharpness of the images is lost and some areas of print are not correctly printed. However, the rate at which such deposits accumulate on rubber-blanket cylinders is particularly high because of high viscosity and the adhesive properties of the printing ink. Thus, for reasons of operating safety, and to maintain print quality, it is essential that dirt and the like is removed from such cylinders on a regular basis.
As a rule, when such deposits are to be removed, the printing process is interrupted and the cylinders are washed by hand. This requires not only a great deal of time--the washing procedure and the interruption of the printing process take about fifteen minutes--but the personnel performing the washing procedure have to proceed with caution in order that no lint from the cleaning rags remain behind on the surface, particularly of rubber-blanket cylinders, for such lint cause foul impressions. In addition, such hand washing is a health hazard for the personnel who perform the washing process, for contact with solvents dissolves the protective covering on the skin and breathing high concentrations of solvent vapours is prejudicial to general health.
Automated printing cylinder washing devices, such as described in EP 0 419 289 A2, have been used of late.
Essentially, the automated washing device described in the above-quoted document comprises a roller brush that can be moved against the cylinder that is to be cleaned, nozzle tubes for spraying the roller brush with washing fluid, feed lines for the washing fluids, and a control system to manage the individual functions. If a plurality of washing devices are used in a printing press, they can be controlled from a central control unit, and this makes it possible to operate such devices by remote control.
The great disadvantage of these known, automated printing cylinder washing devices is the fact that the wash programs cannot be varied. For example, with respect to the individual washing devices, the duration of the cleaning process, the metering of washing liquids, and--above all else--the timing of the washing liquid metering, and the mechanical course of the cleaning process are fixed for the cleaning conditions that are, as a rule, to be expected.
Various operating parameters, for example, the speed at which the cylinders are rotated during the cleaning process, or information as to whether or not there is contact between the cylinder and the material to be imprinted and whether or not this contact is with the face or the reverse side of the material to be imprinted, the volume of production since the last washing, the position of the cylinders in the printing sequence, or the quality of the paper naturally have a great effect on the length of the washing process that will be required, the quantity of liquid required, and, above all else, on the precise sequence followed during the duration of the washing process. If the cylinders are soiled too heavily, or the pre-set wash programs are not designed for the existing operating parameters, the results obtained from the washing process will be unsatisfactory and will lead to poor quality printing when printing operations are resumed, or else the washing procedure will have to be repeated. In addition, in the case of rotary printing presses with a web of material to be imprinted, unsatisfactory results from the washing process can result in the web tearing. It is just as inappropriate if the degree of soiling of the cylinder is less than expected, for the cylinder will become too wet in the course of the cleaning procedure, so that when printing is resumed, there will be a great deal of waste. In the case of web-type printing presses, it can even happen that if it is dampened too much, the web will break. However, the web must at all costs be prevented from tearing, for if it does, the web will have to be re-threaded [relaced], and this generally takes about 20 minutes.
Especially in the case of large printing presses, which incorporate a plurality of printing units and other cylinders, and in the case of web-type printing presses that permit a large number of variations, for example, in the routing of the web, ink application, or cylinder adjustment, it is difficult to see which cylinders have to be cleaned with a particular washing program. In such cases, up to now it has been almost unavoidable that the cylinders are frequently cleaned when there is no need for it, or that additional personnel are required to identify the need for cleaning by way of visual inspection.